The present invention relates to an image-capturing lens which is suitable as an optical system of a solid state image-capturing device such as a CCD type image sensor or a CMOS type image sensor.
In recent years, a cell-phone and a personal computer each being equipped with an image-capturing apparatus are coming into wide use, with high-performance and downsizing of an image-capturing apparatus employing a solid state image-capturing device such as a CCD (Charge Coupled Device) type image sensor or a CMOS (Complementary Metal Oxide Semiconductor) type image sensor.
Because of high density caused by downsizing or an increase of functions in these cell-phone and personal computer, there are increasing demands for further downsizing of an image-capturing lens carried on the image-capturing apparatus, for realizing a small-sized image-capturing apparatus.
As an image-capturing lens for this small-sized image-capturing apparatus, a lens of a structure of three lenses wherein a first lens having positive refracting power, second lens having negative refracting power and a third lens having positive refracting power are arranged in this order from an object side is becoming popular in recent years, because an image-capturing lens of this type can be of higher performance, compared with an image-capturing lens which is of a structure of a single lens or of two lenses. The image-capturing lens of the so-called triplet type of this kind is disclosed in, for example, TOKKAI No. 2001-75006.
However, the image-capturing lens of the type described in TOKKAI No. 2001-75006 has not been suitable for downsizing of a total length of the image-capturing lens (a distance from a surface located closest the object side in the entire image-capturing lens to an image-side focal point, provided that in the image-capturing lens in which the aperture diaphragm is located closest to the object side, the total length of the image-capturing lens is a distance from the aperture diaphragm to the image side focal point), although it is of a type wherein various aberrations are corrected properly while a wide field angle is secured.